Re-add filter setting to PNG metadata.

.vscode/settings.json

@@ -27,6 +27,7 @@
         "iomanip": "cpp",
         "__cxx_version": "cpp",
         "string": "cpp",
-        "type_traits": "cpp"
+        "type_traits": "cpp",
+        "ostream": "cpp"
     }
 }

src/emucore/TIASurface.cxx

@@ -302,6 +302,9 @@ string TIASurface::effectsInfo() const
           << attr.blendalpha;
       break;
   }
+
+  buf << ", filter=" << myOSystem.settings().getString("tia.filter");
+
   return buf.str();
 }